Battles.

Of course, I also considered the hero's parameters when planning the battle, and the advanced tactics are evident from the battlefield. In principle, the tactics could have been replaced with a mass speed boost. The magical properties are not critical – I only cast magic twice, the rest was just melee combat. To reduce losses, it might have been worth dismissing the griffins (replacing them with horses). Archers are mainly for cleanup. Although, in the final battle, I could have sacrificed the army (and done without magic).
For variety, I decided to replay the same situation without magic – I lost 5 horses. Conclusion: "brute force doesn't always work," and magic of levels 1-2 can also be useful :D. By the way, a significant factor can be the enemy's morale dropping, because prematurely freeing blocked grand units increases their attack power by 4 times!